The invention relates to a gas spring having a safety device to prevent against collapse in the event of pressure loss, a volume of gas under pressure is present in a cylinder, and a piston is connected to a piston rod sliding in contact with the inside wall of the cylinder, while the piston rod is guided and sealed at the end of the cylinder where it emerges. The safety comprises a movable partition arranged in the interior of the cylinder and sealed against the inside wall of the cylinder.
Such gas springs are employed, for example, for counterbalancing purposes and to lift flaps, drawing boards and the like. It may happen that the gas spring will lose pressure in the course of time. If in such case the fixation of the drawing board is released, the gas spring pressure will not suffice to compensate the weight of the drawing board with drafting machine, and if the pressure drop is considerable, the drawing board will come down very suddenly. The user is likely to be taken unawares, and bodily harm may result.
To eliminate this hazard, DE-OS No. 2,540,402 discloses the arrangement of a brake, a movable partition being arranged in the gas spring cylinder and acted upon on one side by the internal spring pressure and on the other side by cup springs. Towards the inside of the gas spring, the partition is provided with a longitudinally slit cone, capable of wedging into an annular plate encircling the piston rod. If the pressure in the gas spring diminishes, the cup springs force the cone into the plate. This alters the inside diameter of the cone, so that it comes into locking contact with the piston rod. Such a brake requires an additional seal between partition and piston rod, which is costly and lessens the ease of operation. In addition, the brake acts on the precision-machined piston rod, and there is a danger that the engagement of the cone and the piston rod may damage the latter. Another disadvantage is that the brake release is delayed if the pressure in the spring is increased by supplying gas. Then the unpredictably extended piston rod involves the same safety hazard as the unpredictable descent of the drawing board or flap.